The invention relates to an arrangement for a wall section to be acted on by an impact flow.
Among convection cooling and heating processes, impact cooling or impact heating results in the highest heat transfer values. The impact flow is realized in that a cooling or heating fluid (e.g. air, water, water steam, hydrogen, liquid sodium, etc.) flows through one or more openings in a wall and impacts a facing surface more or less vertically. When impacting the impact surface, the free streams are deflected, and a flow forms parallel to the impact surface, resulting in a high heat transfer between the flow and the wall. To enlarge the heat transfer surface, known solutions provide it with roughness elements, usually in the form of ribs.
An arrangement of the initially mentioned type is known from U.S. Pat. No. 5 321 951. The impacted surface of this document is provided with bulges arranged at regular intervals. The diameter of each bulge is at least as large as its height. The bulges are as a rule smaller than the known ribs or pins and, in addition to increasing the convection surface, are also supposed to create turbulence. The diameter of the bulge elements is small in relation to the diameter of the impact stream, so that an impact stream impacts several bulges at the same time. As a result of the irregular arrangement of the impact openings in the support, local differences in the impact on the impact surface with the bulges occur with a regular arrangement of the bulges.
Another type of impact cooling is known from DE-A-44 30 302. The method described there is characterized by a plurality of impact pipes that are arranged with their inlet in a plane on a flat or curved support and are oriented with their mouth against the wall section to be cooled, whereby the support is arranged at a distance from the wall section. In one exemplary embodiment (FIG. 3), the impact surface of the wall section to be cooled is constructed as a relief, whereby the streams directly impact the projecting bulges. This is supposed to even out the inhomogeneous heat transfer in the impact streams and achieve a homogeneous temperature distribution on the hot side of the wall section. In this arrangement, the bulges are constructed essentially as cylinders with rounded edges created during manufacturing. In another exemplary embodiment (FIG. 4), the relief has the form of ribs. In relation to the thermal transition, both geometries do not have any advantageous thermal boundary conditions. The heat, which can be transferred over the surface of an element projecting from the wall to be cooled, first must be passed through the element""s base surface and the material to the surface. This creates a layering of temperatures in the material of the element. Depending on the material and geometry, this may have the result that at the points furthest away from the base of the element the temperature difference between fluid and element becomes so small that practically no heat transfer takes place any more.
The invention is based on the objective of creating an impact arrangement in which the bulging roughness elements are optimized in respect to the manufacturing process and thermal effectiveness. Based on the above mentioned known bulges, both geometry and their size and arrangement relative to the free streams must be considered for this.
In accordance with the present invention, an arrangement for a wall section to be impacted by an impact stream includes a plurality of impact openings arranged on a plane in a flat or curved support, with said support being arranged at a distance from the wall section. The wall section includes an impact surface to be cooled or heated and is constructed as a relief with bulge elements. The bulge elements are rotational bodies whose forming curve includes first and second curvature sections that merge with each other. And the bulge elements are arranged around the impact surface of the impact stream.
In accordance with another aspect of the invention, the first curvature section ends at the impact surface of the wall section. This curvature section has an angle which forms a circle segment having a radius, whereby the circle segment approaches at least approximately a curve of the form x=y.
According to a further aspect of the present invention, the second curvature section has a radius which extends between two of the first curvature sections. At an intersecting point between the first and second curvature sections, the first and second curvature sections have a mutual tangent that forms an angle xcex2 with respect to a direction normal to the plane of the wall section.
In accordance with an additional aspect of the present invention, each of the bulge elements includes a base, and the size of each base is such that the bases of adjoining bulge elements touch each other.
In accordance with a further aspect of the present invention, the uppermost points of the bulge elements are connected with the support.
According to a further aspect of the present invention, the wall section to be cooled or heated is constructed together with the bulge elements as a cast part.
In accordance with another aspect of the present invention, the impact openings form an inlet of impact pipes, the impact pipes have mouths which are oriented toward the wall section to be cooled or heated.
In accordance with an additional aspect of the present invention, the bulge elements are distributed symmetrically around the impact stream.
The advantages of the new measure are, among others, that as a result of the almost isothermal surface a high pin effectiveness is achieved, and that a high heat transfer is present also on the surfaces that are not oriented parallel to the wall that is supposed to be impacted with the impact streams. Because there are no sharp edges and small radii, a simple and cost-efficient manufacturing can be expected. The geometry can be easily molded and therefore cast; it is fault-tolerant and permits large dimensional tolerances. Because of the symmetry of the bulges, their arrangements does not depend on the incoming flow of the deflected impact agent. Finally, the new bulge elements also have low pressure losses.
The bulge elements also can be used as spacers for the stream-generating plate if this plate rests on the bulges. This measure is known per se, but the special configuration of the bulge elements results in hardly any losses in the heat transfer surface.